1. Field of the Invention
The present invention relates to a seesaw switch for switching on and off in seesaw fashion by a push of a key button at either end thereof.
2. Description of the Prior Art
Conventionally, a seesaw switch used for an automotive power window switch is constructed, for example, as shown in FIGS. 4 and 5.
Referring to FIGS. 4 and 5, a printed board 2 on which various electronic components are mounted is provided in a case 1, and left-hand and right-hand fixed contacts 3a and 3b are formed by a copper pattern as a conductive portion on an upper surface of the printed board 2. Left-hand and right-hand rubber contacts 4a, 4b made of silicone rubber are placed above the fixed contacts 3a, 3b formed on the printed board 2, and left-hand and right-hand pushing elements 5a, 5b, of a T-shaped cross-sectional configuration are placed on the rubber contacts 4a, 4b, respectively.
A rectangular through hole 6 is formed in the case 1 above the rubber contacts 4a, 4b, and support shafts 7 are mounted on front and rear peripheral side surfaces of the through hole 6.
In the case 1 is provided a base 9 having a lower surface defining recesses 10a, 10b receiving upper portions of the rubber contacts 4a, 4b and lower portions of the pushing elements 5a, 5b. The recesses 10a, 10b of the base 9 have through holes formed respectively centrally thereof and receiving shaft portions of the pushing elements 5a, 5b, and upper portions of the shaft portions of the pushing elements 5a, 5b, are directed upwardly of the base 9.
A key button 12 having an exterior dimension slightly smaller than the interior dimension of the through hole 6 is inserted in the through hole 6 from below the case 1, with play held between the key button 12 and the through hole 6. Left-hand and right-hand ends of the key button 12 are placed on the pushing elements 5a, 5b, formed on the rubber contacts 4a, 4b, respectively. The key button 12 has front and rear peripheral surfaces defining apertures 13 receiving the support shafts 7 so that the key button 12 is supported for seesaw operation.
A light emitting device 14 is provided between the fixed contacts 3a and 3bon the printed board 2 and housed in a receiving recess formed in the base 9. The light emitting device 14 illuminates a light-pervious window portion of a character-shaped configuration formed on an upper surface of the key button 12.
In such an arrangement, pushing the key button 12 at its left-hand end against the elasticity of the rubber contact 4a permits the key button 12 to pivot on the support shafts 7 in the pushing direction, and the key button 12 presses and deforms the rubber contact 4a through the pushing element 5a. Then a conductor 16a bonded on the rubber contact 4a comes into contact with the fixed contact 3a, and electrical connection is made between the conductor 16a and the fixed contact 3a. Pushing the key button 12 at its right-hand end provides similar operation wherein a conductor 16b comes into contact with the fixed contact 3b and electrical connection is made between the conductor 16b and the fixed contact 3b.
The interior dimension of the through hole 6 is slightly greater than the exterior dimension of the key button 12 so that the left-hand and right-hand ends of the key button 12 when pivoted do not contact the peripheral surfaces of the through hole 6, and the key button 12 is inserted in the through hole 6, with play held therebetween.
Another conventional seesaw switch is shown in FIGS. 6 and 7. The differences from the construction of FIGS. 4 and 5 are described below. A guide wall 18 extending downwardly is formed integrally with the case 1 on the periphery of the through hole 6. The guide wall 18 includes a partition board 19 for closing the lower opening of the guide wall 18, and a rectangular through hole 20 for housing the light emitting device 14 is formed centrally of the partition board 19. Through holes 21a, 21b for the shaft portions of the pushing elements 5a, 5b, are formed on the left and right of the through hole 20 of the partition board 19, and the upper portions of the shaft portions of the pushing elements 5a, 5b, are directed through the through holes 21a, 21b upwardly of the partition board 19 for abutment against the left-hand and right-hand ends of the key button 12, respectively.
However, the foregoing arrangements necessitate the provision of the shafts 7 on the front and rear peripheral side surfaces of the through hole 6. The techniques of providing the shafts 7 include forming the shafts 7 from separate members and forming the shafts 7 by using a sliding die for forming the through holes 13 of the key button 12. On the other hand, a sliding die for forming the shaft holes in the case 1 is used to provide the shafts 7 on the key button 12. Forming the shafts 7 from the separate members results in an increased number of components, and forming the shafts 7 by using the sliding die results in increased costs of the die.
Another drawback is that the provision of the light emitting device 14 for character illumination causes the through hole 6 to have the interior dimension greater than the exterior dimension of the key button 12, resulting in light coming outwardly through the gap-between the case 1 and the key button 12 when the switching operation is not being performed.